By Eamonn Ryan
The sweet success of perfectly ripened bananas relies on a delicate dance of temperature, humidity and, crucially, airflow.
Bracken Refrigeration Services (BRS) has successfully completed a significant in-house agricultural facility project, DCS-ZIRE which is part of the Subtropico Group – a fresh produce centre with cold rooms, ripening rooms and a fully functional distribution centre in north Pretoria.
The project involved the design and installation of a sophisticated ethylene- ripening and Farmwise packing facility within the same building – primarily for bananas, but also a wide variety of produce including apples, oranges and avocados.
The project, spearheaded by Bracken Refrigeration Services project manager Morné Seymore, commenced with an initial requirement for 23 ripening rooms in mid-March 2020 and reached completion within approximately five months, despite challenges posed by the initial stages of the COVID-19 pandemic. This included brief work stoppages due to both material shortages and COVID-19 related compliance requirements, however the project progressed steadily from its March 2020 start to its conclusion in August/September of the same year, including a final month to address minor snags.
Following the successful completion of the initial phase in 2020, this collaboration between Bracken Refrigeration and DCS- ZIRE Subtropico continued into a second phase in 2022, followed by this current third phase.
Seymore explains that the project was specifically initiated to create a dedicated environment for ripening a substantial quantity of bananas. “The core focus was to efficiently ripen the bananas. However, the scope of the project expanded over time to encompass a packing area within the same building, streamlining the post- harvest process. The facility also includes a specialised holding area equipped with a cooling system designed to bring the produce down to precise temperatures before being moved via a conveyor system for further processing.”
Another significant obstacle was the sourcing of copper fittings. Faced with supplier issues, the BRS team had to adapt by themselves, designing and fabricating T-fittings for the copper pipes directly on-site. This resourceful solution not only kept the project on track but also deeply impressed the client, with the custom fittings reportedly still in perfect working order.
Purpose-built innovation
Subtropico’s decision to establish a state- of-the-art banana ripening facility stemmed directly from the significant challenges faced by banana producers in South African produce markets. Traditional, often publicly-owned, ripening facilities proved inadequate due to their inefficiency and poorly maintained water-chilled plant systems. This resulted in substantial losses and frequent insurance claims for Subtropico, which handles a high volume of bananas nationwide. Prompted by these limitations, Subtropico’s management opted to build brand-new, purpose-built ripening infrastructure.
The design for this facility was precisely tailored to DCS-ZIRE Subtropico’s requirements for efficient banana ripening, based on the volume of bananas needing to be processed within a specific timeframe
Leveraging a standard of 30kW cooling capacity for a 30-pallet ripening room, BRS collaborated closely with Metraclark and validated the refrigeration system’s cooling capacity based on BRS’s projections.
The rapid success of the initial phase comprising 23 ripening rooms, however, quickly exposed the facility’s immediate need for expansion, as even 23 rooms proved insufficient for the rapidly growing banana volumes. All rooms were consistently full, leading to an immediate demand for eight new rooms, and a subsequent third phase ultimately increased the total number of ripening rooms to 42.
Switches in equipment came as and when alternative products were deemed to offer comparable quality at a more favourable price point. Airflow within the ripening rooms was a critical consideration, leading to an upgrade in fan capacity. “We upgraded the fans from 0.75kW to 1.1kW to give us a bit more airflow in the rooms,” Seymore explains. These higher-capacity fans were supplied by AMS (Air Movement Supplies).
Beyond the core refrigeration components, the facility incorporated a range of other essential equipment. BRS manufactures the electrical DB boards in-house. The crucial control system, responsible for regulating temperature, humidity, ethylene levels (essential for ripening) and CO2, was sourced from CAREL. Dixell Controllers were also integrated into the system. Seymore noted a long-standing relationship with CAREL for customised control systems, allowing for tailored solutions to meet specific client needs. A commitment to long-term performance and minimising potential issues for their clients drives their choice of suppliers.
Electrical components, including switchgear, were supplied by RA Distributors, a local South African company known for its quality ACDC-branded products. BRS handles the wiring and testing of the DB boards at their facility before shipping them to the site for installation. The insulated panels forming the structure of the ripening rooms were supplied and installed by Panelman Engineering in Rosslyn, Pretoria. These panels were specified as 100mm thick with a density of 15DV and a standard white chromadek exterior with aluminum finishing. Access to the ripening rooms is facilitated by Stab-a-Load sectional vertical lifts and motorised doors, which also feature a manual override for operation during power outages, a practical consideration in the South African context.
The DCS-ZIRE Subtropico facility utilises a 30kW system featuring a split condensing unit, which they refer to as a ‘receiver set button on’ with the receiver set on the roof. This configuration places the compressor and receiver unit inside the building, typically on top of the ripening rooms, while the condenser unit is located externally.
Inside the ripening rooms, dual discharge coils are employed, either from HC Group or Metraclark. This design ensures efficient and even cooling by blowing air outwards from the sides of the unit, circulating it through the stacked bananas, and drawing air back in from the bottom. This system – designed by BRS many years ago – has proven highly effective over the years of installations across South Africa, as well as across southern Africa.
Seymore states that there were “actually no challenges” beyond the initial COVID-19 related delays. This is due to the team’s extensive experience with such installations, and even in the event of technical issues, such as a control system malfunction, suppliers like CAREL are known for their prompt on-site support, often responding the same day.
Minimising power consumption is a significant benefit for the client, hence the use of Copeland scroll compressors in many applications compared to older compressor types which, given there were ultimately 42 rooms, delivered considerable energy saving. Seymore highlights the challenge of finding a 1.1kW fan that delivers the same airflow as current models but with significantly lower energy usage. For the DCS-ZIRE Subtropico project, energy efficiency was also addressed through the implementation of lower voltage (12 volt DC) systems for certain control components and the use of LED lighting throughout the ripening rooms, contributing to a reduction in overall energy consumption.
The scale and the significance of the project and client, Subtropico, are what make this project unique to BRS. Seymore explains: “You rarely get 23 rooms in a single project – even 10 would be a large project, and then to complete it in five months is something we’re proud of.”
Airflow as the heart of uniform ripening
Achieving that ideal, consistent ripeness in bananas demands far more than merely controlling temperature. As Seymore emphatically states, “Precise airflow management is paramount to consistent results.” This philosophy underpins the advanced ripening techniques at play.
The prevailing challenge in many facilities stems from inadequate airflow control. Simply boosting refrigeration capacity, without concurrently addressing how that cool air is distributed, inevitably leads to a mix of overripe, optimally ripe and still-unripe fruit within the same batch. This inconsistency directly impacts quality and profitability.
In stark contrast, state-of-the-art ripening rooms are designed to guarantee uniformity. This means every banana within a specific batch achieves the same desirable colour and ripeness, irrespective of its position on a pallet – whether at the front, middle, back, top or bottom.
The cornerstone of this consistency lies in meticulously engineered and forcefully delivered airflow. This seemingly straightforward concept is, in fact, critical. The packaging of the bananas also plays an integral role; boxes feature specially designed perforations that align perfectly when stacked on pallets. This alignment creates a powerful and uniform atmosphere throughout the entire ripening room. The intensity of the top-down airflow is so significant that, unlike conventional systems, one can distinctly feel the air emanating from within a box even when positioned midway through a stacked pallet. This integrated design, combining robust forced airflow with precisely perforated boxes, ensures an even and effective distribution of the crucial ripening atmosphere.
The specialised knowledge of Riaan van
der Merwe, owner of BRS, a refrigeration expert with extensive experience in the banana industry, was pivotal in achieving this precise airflow management. Van der Merwe’s deep understanding of air changes and airflow dynamics, stemming from his involvement with the Banana Board in the 1970s and 80s, was invaluable. Instead of relying on standard recommendations, he specified particular coils with stainless steel components and insisted on using AMS fan motors with a defined output and airflow specification. This necessitated a redesign of a custom coil to precisely match the airflow characteristics of the specified AMS fans and the required cooling capacity.
This collaborative approach resulted in a custom-designed evaporator coil, optimally paired with the AMS fan airflow to maximise cooling efficiency and air changes. In essence, the evaporator needed to be strategically sized to effectively harmonise with the specific airflow requirements.
The installation incorporated a strategic approach to condenser placement. The entire side of the building features remotely located condensers. This remote configuration was chosen to mitigate potential challenges associated with housing all condenser units externally, such as structural weight considerations and excessively long refrigerant pipe runs. BRS therefore opted to install receiver sets to be positioned above each room, and the corresponding condensers located remotely on the same level as the receiver set along the building’s exterior. These receiver sets, utilising Copeland compressors, effectively addressed these logistical and engineering considerations.
The air-conditioning component
Beyond the critical refrigeration systems designed for precise fruit ripening, the facility also incorporated significant air- conditioning infrastructure to maintain optimal environmental conditions within the pre-cooling and boxing areas utilised by Farmwise. The detailed ductwork design for this system was handled by BRS.
Seymore says: “We also supplied the air conditioning rooftop package units for these zones. Specifically, we provided four air-cooled rooftop packages, each with a capacity of 240 000 BTUs, to service the areas not enclosed within insulated panels.”
This resulted in a substantial air-conditioning capacity, totaling approximately 960 000 BTUs or 281kW. These units were described as “off-the-shelf, eco rooftop package units that we import under the brand name ‘Echo'”. While acknowledging the possibility of slight oversizing, the primary design consideration was ensuring adequate airflow throughout these large processing spaces. “We opted for slightly larger units to guarantee the necessary airflow.”
The processing area is characterised by conveyors and other equipment, with a network of rigid ducting with air distribution grilles overhead, to achieve a comfortable and controlled environment suitable for pre-cooling and packaging operations.
This resulted in a completed installation, showcasing the four package units mounted on support frames with meticulously installed rigid ductwork extending into the building.
